1. Field of the Invention
This invention relates to a digital signal transmitting and/or receiving system and more particularly is directed to a digital signal transmitting system for transmitting a digital signal, which results from A/D (analog-to-digital)converting a stereo signal or emergency broadcast signal, through a CATV (cable television) transmission line.
2. Description of the Prior Art
A system has been proposed in the art in which time division-multiplexed digital audio signals of a plurality of channels are transmitted by using a vacant channel of a CATV transmission line. According to such transmission system, a stereo broadcast of high quality having a wide dynamic range or emergency broadcast becomes possible. In this case, in order to discriminate whether the broadcast is the stereo broadcast or emergency broadcast, a mode change-over signal is time division-multiplexed with a word synchronizing signal and a digital audio signal as a 4-bit service bit signal and then transmitted. At a receiver side, the service bit signal is decoded and used as a control signal for controlling a playback mode of a desired digital audio signal.
However, upon emergency broadcast, although it is desired that a power source of a television receiver is turned on, a receiving channel of the television receiver is changed over into an emergency broadcast channel and the emergency broadcast is received by the television receiver, such system has not yet been proposed.